1. Field of the Invention
The present invention relates to a valve timing adjuster for controlling valve timing of a valve that is opened and closed by a camshaft through torque transmitted from a crankshaft in an internal combustion engine.
2. Description of Related Art
A conventional valve timing adjuster is known to include a housing and a vane rotor and is known to adjust valve timing using hydraulic oil supplied from a supply source, such as a pump. For example, in an apparatus of JP-A-2002-357105 corresponding to US2002/0139332, a vane rotor in the housing has vanes that define advance chambers and retard chambers arranged one after another in a rotational direction (circumferential direction), and the apparatus adjusts valve timing by changing the rotational phase of the vane rotor relative to the housing in an advance direction and in a retard direction by supplying working fluid to the corresponding chambers.
The apparatus of JP-A-2002-357105 is designed such that the rotational phase is to be regulated to a regulation position located between a full advance position and a full retard position by bringing a regulation member, which is supported by the vane rotor, into engagement with the vane rotor. In the configuration above, the regulating of the rotational phase to the regulation position at the stopping of the internal combustion engine makes it possible to maintain the rotational phase to the regulation position at the starting of the internal combustion engine in the next operation, and thereby it is possible to achieve the engine startability.
In the apparatus of JP-A-2002-357105, in a case, where the internal combustion engine under operation instantly stops due to the occurrence of abnormality, the internal combustion engine may stop before the rotational phase is regulated to a regulation position. If cranking of the internal combustion engine starts after the above abnormal stop of the engine in a condition, where the rotational phase is located at a position different from the regulation position, the amount of intake air to the engine may not be appropriate, and thereby the engine startability may deteriorate disadvantageously.
The inventors have intensively studied a technique that shifts the rotational phase back to the regulation position by using variable torque (torque reversal) that is applied from the camshaft to the vane rotor at the time of engine start through cranking of the internal combustion engine. As a result, the inventors have found that the rotational phase is less likely to be shifted back to the regulation position under a low-temperature environment. More specifically, under the low-temperature environment, the degree of viscosity of working fluid is increased, and thereby the introduction of the working fluid into each chamber may be delayed. Thus, the variable torque (torque reversal) enlarges the volume of the advance chamber or the retard chamber at the time of starting the internal combustion engine, and thereby negative pressure may be disadvantageously generated for disturbing the movement of the vane rotor. As a result, the rotational phase becomes less likely to be shifted back to the regulation position under the low-temperature environment.